[Mochichimaru] My Busty Childhood Friend and Big Bro Have Been Acting Weird Lately [Nisor]

Mizuki, a busty childhood friend in her school uniform, is supposed to be the narrator's girl—until "Big Bro" steps in, kissing her and pinning her down while she gasps "Mizuki... you're the only one for me now, Daichi-kun..." and begs him to pound her rougher and deeper. The younger brother secretly watches from the trash, discovering a tied-off bag of used condoms with a horrified "No way... isn't this..." and a stolen "A condom?!" breath, sealing his spiral into voyeuristic arousal and lonely, conflicted release.